1. Field of the Invention
The present invention relates to a coded division multiple access (CDMA) receiver for use with a mobile communication system of CDMA type and a method of judging transport format combination indicator (TFCI) candidates of the same.
2. Description of the Prior Art
In a CDMA receiver described, for example, in “W-CDMA Mobile Communication Method” supervised by Keiji Tachikawa and published from Maruzen, a data decoding operation is conducted by a decoder unit including constituent components generally shown in FIG. 2 such as a wireless frame combining section 31, a primary interleaving section 32, a rate matching section 33, an error correction and decoding section 34 for viterbi and turbo decoding schemes, and a cyclic redundancy check (CRC) unit 35. The operation requires transport format information indicating a block size and the number of blocks for a unit of data to be decoded. The transport format information is determined for each channel called a transport channel and takes a value variable with a period called a transmission time interval. This interval has a value represented by an integral multiplex of a wireless frame length. The length is a minimum value of the data unit for a wireless interface.
In a wireless zone, a plurality of transport channel are multiplexed for transmission, and hence a wireless frame thus transmitted includes a transport format combination indicator (TFCI) in addition to the information signal. The indicator includes a value to indicate a combination of format information of each transport channel. When a TFCI signal is received, it is required for the decoder of the CDMA receiver before starting the decoding operation to check the TFCI signal to determine the format information necessary for the decoding of signals on each transport channel.
TFCI is represented by a number identifying a data transmission format, i.e., a data block size and the number of blocks. This means that the TFCI number determines a data rate. According to the standards of the third generation mobile communication system stipulated by the 3rd generation partnership project (3GPP), TFCI is indicated by one of 1024 numbers ranging from 0 to 1023 and is converted for transmission into a code word (TFCI code sequence) corresponding to each associated number.
In the CDMA receiver having received the TFCI signal, the decoder unit obtains 1024 correlation values between the TFCI code sequences of the predetermined 1024 kinds and the TFCI signal actually received and determines a maximum value of the correlation values to obtain a number corresponding to the correlation value. The decoder regards the number as that of the received TFCI. The decoder then decodes data according to a transport format identified by the TFCI number.
The TFCI signal is mapped onto one 30-bit code word and is decoded according to the Reed-Muller code system for transmission. The TFCI decoding algorithm cannot determine whether or not the decoded TFCI is correct. In other words, even when the TFCI is decoded in a wrong way, the system carries out the decoding operation on assumption that the obtained TFCI indicates a correct state of each channel for a wireless frame. Therefore, the decoder uses wrong multiplexing parameters and conducts the rate matching and the error correction and decoding operation in a wrong way. As a result, the wireless frame data of each transport channel is lost. The error is detected only by the subsequent step of the CRC unit.
In this connection, Japanese Patent Laid-Open Ser. Nos. 2002-246949 and 2003-32146 describe inventions to increase signal receiving precision.
As above, The TFCI decoding algorithm cannot determine whether or not the decoded TFCI is correct. There consequently arises a problem that the system executes the processing in a wrong way using the wrong TFCI, and hence the wireless frame data is lost for each transport channel.
Retransmission of wireless frame data lowers efficiency of use of wireless resources.